Metallurgical operations on metals rely on the movement of certain elements within the solid matrix of the metal to be treated. Metallurgical operations rely on chemical reaction between elements which may be physically brought together or may be induced to come together by diffusion. An element is any chemical element or substance listed in the periodic table. Elements move within the solid metal by a process of diffusion. Diffusion is encouraged when an element is attracted to another element with which it is more reactive within the same contiguous metal structure. Diffusion also occurs when metals tend to form a more homogenous solid solution. Diffusion of an element within a metal is aided by increasing the temperature of the metal. Transfer of an element from one metal to another or from a gaseous atmosphere into a metal or out of a metal also takes place when the materials are in intimate contact. The employment of precise low pressures is often desirable to assist in this transfer.
Nitriding and carburizing are examples of metallurgical operations in which elements are diffused into the surface of the metal. Annealing, solution treatment, tempering and normalizing are examples of heat treat operations in which internal diffusion takes place.
It is frequently desired to modify the internal structure of tiny particles of metal by diffusing an element into the surface. This invention relates particularly to diffusion of elements such as nitrogen, boron, oxygen, carbon, selenium and palladium which in small amounts cause major change in the properties of metals into which they are diffused. In the case of manufacture of titanium aluminides for instance, it may be desirable to diffuse small amounts of nitrogen into the surface of micron sized particles of titanium to form strong intermetallic compounds with the titanium. These particles may then be blended with pure titanium metal particles and the resulting mass can be extruded to form a macro-homogenous structure having tiny hard particles mixed amongst the softer more ductile particles to provide a new composite metal which combines the high strength of the hard particles with the ductility of the softer particles.
In the purification of certain reactive metals (as indicated in the periodic table) such as tantalum, it is desired to remove all oxygen. It has been demonstrated that a metal such as tantalum having small amounts of oxygen mixed therein, if placed in contact with a more oxygen reactive metal, such as yttrium, in the presence of high temperature and the absence of any oxygen in the atmosphere, will result in the yttrium absorbing the oxygen from the tantalum, thereby purifying the tantalum to a greater degree than is possible with any conventional refining process.
With some processes the transfer of elements may be assisted by employing a second solid material as a catalyst. For instance, it may be desirable to expose certain particles to a gaseous atmosphere containing a desired active element and in order to aid the release of this active element, a third solid material may be introduced so that when all three are in intimate contact with each other, the active element in the gas or the active element in the third material will act as a catalyst to aid the transfer or chemical reaction between the other two materials.